Carbon Compounds in Cells

Chapter 3

Importance of Carbon

Carbon permeates the world of life—from the energy-requiring activities and structural organization of cells, to physical and chemical conditions that span the globe and influence ecosystems everywhere.

Humans and Global Warming

• Fossil fuels are rich in carbon

• Use of fossil fuels releases CO2 into atmosphere

• Increased CO2 may contribute to global warming

Organic Compounds

Hydrogen and other elements covalently bonded to carbon

Carbohydrates

Lipids

Proteins

Nucleic Acids

Carbon’s Bonding Behavior

• Outer shell of carbon has 4 electrons; can hold 8

• Each carbon atom can form covalent bonds with up to 4 atoms

Methane: Simplest Organic Compound

Structural formula

Ball-and-stick model

Space-filling model

HH

H

H

C

Figure 3.2Page 36

Bonding Arrangements

• Carbon atoms can form chains or rings

• Other atoms project from the carbon backbone Glucose

(ball-and-stick model)

In-text figurePage 36

Hemoglobin Molecular Models

Ball-and-stick model Space-filling model

Ribbon modelFigure 3.3Page 37

Functional Groups

• Atoms or clusters of atoms that are covalently bonded to carbon backbone

• Give organic compounds their different properties

Examples of Functional Groups

Methyl group - CH3

Hydroxyl group - OH

Amino group - NH3+

Carboxyl group - COOH

Phosphate group - PO3-

Sulfhydryl group - SH

Carbohydrates

Monosaccharides(simple sugars)

Oligosaccharides(short-chain carbohydrates)

Polysaccharides(complex carbohydrates)

• Most include fatty acids– Fats– Phospholipids– Waxes

• Sterols and their derivatives have no fatty acids

• Tend to be insoluble in water

Lipids

Phospholipids

• Main component of

cell membranes

• Hydrophobic head

• Hydrophilic tails

Fig. 3.14a,bPage 43

Sterols and Derivatives

• No fatty acids

• Rigid backbone of

four fused-together

carbon rings

• Cholesterol - most

common type in

animals

Figure 3.15aIn-text p43

Cholesterol

Waxes

• Long-chain fatty acids linked to

long-chain alcohols or carbon

rings

• Firm consistency, repel water

• Important in water-proofing

Protein Synthesis

• Peptide bond

– Condensation reaction links amino group of

one amino acid with carboxyl group of next

Water forms as a by-product

Fig. 3.18aPage 45

Primary Structure

• Sequence of amino acids

• Unique for each protein

• Two linked amino acids = dipeptide

• Three or more = polypeptide

• Backbone of polypeptide has N atoms:

-N-C-C-N-C-C-N-C-C-N-

Second and Third Levels

• Hydrogen bonding

produces helix or

sheet

• Domain formation

Secondary structure

Tertiary structure

Figure 3.19aPage 46

Fourth Level Structure

Some proteins

are made up of

more than one

polypeptide

chain

HLA-A2 quaternary structureFigure 3.20Page 47

Hemoglobinalpha chain

beta chain alpha chain

beta chain

• Sugar

• At least one

phosphate group

• Nitrogen-

containing base

Nucleotide Structure

ATP

Figure 3.23aPage 50

Nucleotide Functions

• Energy carriers

• Coenzymes

• Chemical messengers

• Building blocks for

nucleic acids

DNA

• Double-stranded • Sugar-phosphate

backbone• Covalent bonds in

backbone• H bonds between

bases

Figure 3.25Page 51

RNA

• Usually single strands

• Four types of nucleotides

• Unlike DNA, contains the base uracil in place of thymine

• Three types are key players in protein synthesis